Prior art fuel injector nozzle bodies have a valve guide bore in which a needle valve is reciprocated between open and closed positions with respect to an interior valve seat shaped as a frustrum of a cone. The valve seat is spaced from an injector nozzle body sack in communication with fuel holes for distributing the fuel. Injector nozzle bodies have had a hemispherically configured sack region formed the nozzle downstream of the seat to supply fuel to the spray holes when the needle valve is opened. In the past the small diameter end of the valve seat was established by the dimensions of the sack region and was such that metal grinding could be used to finish such valve seats.
Machining methods of U.S. Pat. Nos. 2,377,159 and 3,783,225 disclose use of cone-shaped electrodes to remove material from a workpiece to form a shaped hole in the workpiece. There is no suggestion of apparatus or methods including combined grinding and non-contact machining to form a sackless fuel injector nozzle body with a precision formed valve seat.
U.S. Pat. Nos. 3,072,777 and 3,614,371 disclose apparatus for moving a non-contact machining electrode transversely of a workpiece to form an opening therein. The apparatus does not include means for concurrently grinding and non-contact machining two or more workpieces by the apparatus and method of the present invention.
Anticipated emission regulations require reduction of such emissions by requiring that sacks of fuel injector nozzles be reconfigured to a V-shape to have a reduced fuel containing space in the nozzle when the valve needle closes while retaining a valve seat configured as a frustrum of a cone. Such reconfigured sack regions result in a significant reduction in the small end diameter of the valve seat. Consequently, the small end diameter of a conical grinding wheel used to grind the seat also is reduced in diameter significantly. As a result, the surface speed of the abrasive grains in the small end diameter of the conical grinding wheel is too low for efficient grinding.